A technique has been developed to study the histochemical localization of peroxidase in Vitis vinifera by blotting freezing/thawing tissue sections on nitrocellulose membranes. After being stained with 4-methoxy- α -naphthol and H2O2, peroxidase-mediated reaction products in mature `Gamay' grapes were seen principally in the skin and, to a lesser extent, the pericarp, where discrete areas of reaction products were located in the vascular bundles. However, for immature `Gamay' and `Grenache' grapes, peroxidase activity in the skin was low and similar to that found in the pericarp. With this technique, fruit vascular bundle structure was preserved. The reliability of the technique in the histochemical localization of peroxidase in grapes was confirmed by fractionation and determining the peroxidase activity in the various tissues.
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